The new controller of BBC1 has described the decision to approach Mariella Frostrup to front an edition of Panorama as a "joke", apparently without realising that the presenter had already been signed up.

Lorraine Heggessey said Ms Frostrup would not be appropriate because presenters of the BBC's flagship current affairs show should have "serious journalistic credentials" - Ms Frostrup is more known for her velvet-voiced TV commercials than hard-edged journalism.

Yet on the day the interview appeared, the BBC confirmed that Ms Frostrup would present a Panorama investigation into the phenomenon of Big Brother-style reality television programmes. The gaffe is an embarrassment for Ms Heggessey, who was only appointed to the position last week.

The BBC attempted yesterday to limit the damage caused by her comments, saying she had not been involved in the decision to approach Ms Frostrup. But some BBC figures privately welcomed her remarks, since they appear to display her commitment to serious journalism on BBC1. There had been fears that the channel would become too entertainment-led, under plans to reposition the BBC's television stations.

In the interview with the Daily Telegraph, Ms Heggessey was asked about the idea to approach Ms Frostrup, which was first revealed by the Guardian. She replied: "Mariella's a talented broadcaster but I'm not sure she'd be right for Panorama. I don't know if anybody really did suggest it, but if they did, it was probably said as a joke. The presenter should always be someone with serious journalistic credentials."

Yesterday, a spokeswoman for the BBC confirmed that Ms Frostrup would present an edition of Panorama as a "one-off". She said: "Lorraine has not yet started as controller of BBC1, and this is not her commission. The decision was taken before she was involved."

Ms Heggessey was making the point that "people with the right credentials" should front all programmes.

The BBC insisted Ms Frostrup, with her background in arts and cultural programming - she is a former presenter of a film review show on Channel 4 and fronted the BBC's Edinburgh festival coverage - made her suitable to report on the impact of programmes like Big Brother.

The decision to approach Ms Frostrup, made at a time when the BBC is attempting to revive Panorama's flagging ratings, raised eyebrows among senior figures at the programme.

In unpublished comments during the same interview, Ms Heggessey did not deny reports that the BBC might reduce Panorama's length from 40 minutes to half an hour. The annual run has been cut from 38 to 30 programmes and the budget increased by £100,000 in an attempt to revive the show.